Dear Snowdownia,
Well, my things arrived here in the UK last week, nearly 6 years after I left the US and, thankfully, I did not have to pay any tax or duty. Generally speaking, one has 12 months during which one may import personal goods into the UK (nothing newly purchased for the purpose).
There are forms that must be completed and affixed to your crates and in some cases, like mine, when one is requesting tax relief, one can submit a personal statement explaining why you have taken so long. In my case, it worked.
Here is a link to the HMRC guide:
http://www.hmrc.gov.uk/customs/arriving/moving.htmUnfortunately, the HMRC guides generate more questions than you started with, just keep looking because individual tax rates depend on a variety of factors; are they antique (over 100 years old), art works, inherited within a specific time &c. Your transport company should have good advice but do your own as well.
Good luck and be prepared for cold weather!